Choose the correct alternative which will improve the quoted part of the given sentence.
We demonstrated to them how we 'were prepared' the drawings.

Correct option is C

The correct substitution is: “had prepared”.
Explanation:
The sentence talks about a past action completed before another past action, which is where past perfect tense should be used — “had prepared.”
“Were prepared” would be incorrect because it implies passive voice or continuous tense, which does not suit the structure.
Grammatical Rule Used:
When one past action preceded another past action, we use Past Perfect (had + V3).
Explanation in Hindi:
जब दो घटनाएँ भूतकाल में हुई हों और एक घटना दूसरी से पहले हुई हो, तो पहले हुई घटना के लिए “Past Perfect” (had + V3) का प्रयोग करते हैं।
इसलिए सही वाक्य होगा – “how we had prepared the drawings.”
Example:
He told us how he had solved the problem.